v3.20.1

Business combination - Consideration Transferred (Details) - WageWorks, Inc. - USD ($) $ in Millions		12 Months Ended
	Aug. 30, 2019	Jan. 31, 2020
Business Acquisition [Line Items]
Fair value of previously owned investment in WageWorks stock		$ 81.4
Total consideration paid	$ 2,000.0	2,122.1
Common stock
Business Acquisition [Line Items]
Aggregate fair value of WageWorks stock acquired		2,018.8
Pre-acquisition Equity Awards
Business Acquisition [Line Items]
Fair value of equity awards exchanged for cash attributable to pre-Acquisition service		18.1
Fair value of equity awards replaced attributable to pre-Acquisition service		18.1
Equity Awards Assumed Attributable To Pre Acquisition Service
Business Acquisition [Line Items]
Fair value of equity awards exchanged for cash attributable to pre-Acquisition service		3.8
Fair value of equity awards replaced attributable to pre-Acquisition service		$ 3.8

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